The delicate balance of hormonal influences that governs gonadotropin production by the pituitary gonadotrope cell includes activin and follistatin (derived from the gonad and from the gonadotrope itself), the pulsatile pattern of the hypothalamic releasing hormone, GnRH, and gonadal steroid hormone feedback. In Research Project I, our focus will be the cellular and molecular mechanisms of activin, GnRH, and steroid hormone regulation of LH and FSH beta-subunit gene expression in the gonadotrope. Our model system is the mouse, due to the facile manipulations of the genome attainable by genetic technology and the ability to exploit our immortal mouse gonadotrope cell lines that express FSH, LH, activin, follistatin, and the receptors for GnRH, activin, androgens, glucocorticoids, and progestins. In Specific Aim 1, we will focus on the induction of the FSH and LH beta-subunit genes by activin and the physiological role of activin signaling in the gonadotrope in vivo in Smad deficient mice. In Specific Aim 2, we will investigate the molecular mechanism for tonic and pulsatile regulation of the LH and FSH beta-subunit genes and study the dependence of GnRH action on the activin autocrine loop in culture. In Specific Aim 3, we will address the roles of steroid hormone signaling in regulation of the FSH beta-subunit gene in culture focusing on androgens, glucocorticoids, and progestins. As is the case for GnRH, steroid hormone induction of the FSH beta-subunit gene is dependent upon activin autocrine tone in the gonadotrope and synergistic with induction by activin. We will investigate the basis of this interaction at the molecular level. Finally, we will utilize targeted disruption of the steroid receptor genes in the gonadotrope in mice to assess the role of these receptors in the pituitary in vivo. Our overall goal is to address the integration of activin, GnRH, and steroid hormone signaling in the regulation of LH and FSH in the gonadotrope. Thus, the interplay of peptide hormones, growth factors, steroids, receptors, and hypothalamic releasing factors in controlling gonadotropin gene expression will be investigated using the armamentarium of molecular, cellular, genetic, and mouse technologies with the goal of developing a detailed understanding of the molecular mechanisms mediating reproductive function at the level of the pituitary.